Transplanting Iris Bulbs

The correct method for transplanting iris bulbs depends on the type of iris involved. There are two broad divisions known as bulbous and rhizomatous. The bulbous type, as its name suggests, grow from bulbs and comprise most of the English and Dutch iris varieties. On the other hand the rhizomatous type have rhizomes which are horizontally growing underground stems that are used as food storage for the plant. The common bearded iris falls into this group as well as the beardless Siberian and Japanese iris.

The bulbous irises can be transplanted when the foliage has wilted after flowering. Before transplanting iris bulbs prepare the ground thoroughly by digging and forking in some compost or other organic material together with some general fertilizer.

The rhizomatous irises are best transplanted in late summer from July to the end of September. This type tends to grow into a large clump and after three or four years produce less flowers. The clump will need to be divided at this time and replanted.

When transplanting iris bulbs, first cut back the leaves to about one third of their height. Lift the entire clump with a spade or digging fork. Use a sharp knife to separate the rhizomes. The new transplants should have a firm rhizome with roots and a fan of leaves. Remove and discard the old rhizomes and only replant the younger smaller rhizomes that grow off of the older stems.

Before replanting you should dig in some organic material to improve the structure of the soil and aid drainage. Do not plant the new sections too deep but allow part of the rhizomes to remain uncovered by soil.